1. Field of the Invention
The invention relates to a working vehicle such as an agricultural tractor.
2. Description of the Related Art
Regarding a working vehicle of the related art, for example, JP-A-2004-196106 discloses a configuration of a hydraulic circuit of a power vehicle including an engine mounted on a vehicle body having front wheels and rear wheels, a transmission case, in which a transmission having driving mechanisms including a variety of clutches and gear mechanisms for speed-changing a rotational speed of the engine to appropriate rotational speeds of the front and rear wheels in accordance with a traveling state, is accommodated, and a hydraulic pump for supplying an operating oil to the various driving mechanisms, wherein a decompression valve, which introduces a high-pressure oil from the hydraulic pump through an external oil passage and divides and outputs the same into a specified pressure and a surplus pressure, is provided on one sidewall of the transmission case, a first control valve (a 4WD valve) is attached to the decompression valve, a second control valve (a main change valve, a Hi-Lo switching valve) and a third valve (a reverser valve, a valve for automatic turning) are provided on the other sidewall of the transmission case and a supply oil passage to the first control valve, the second control valve and the third control valve is connected to a specified pressure-side oil passage of the decompression valve.
Also, JP-A-2008-95748 discloses a transmission of a tractor speed-changing and transmitting power from a driving source to driving wheels, which transmission has a main shift shaft, a pair of advancing and reversing hydraulic clutch mechanisms, two sets of first and second change speed mechanisms of a gear synchronizing type and a pair of first and second hydraulic clutch mechanisms. In this case, the main shift shaft is arranged in parallel with an input shaft. The pair of advancing and reversing hydraulic clutch mechanisms is arranged on the input shaft and switches a rotating direction of power transmitted to the main shift shaft. The two sets of first and second change speed mechanisms of a gear synchronizing type are arranged on output-sides of the pair of advancing and reversing hydraulic clutch mechanisms. The pair of first and second hydraulic clutch mechanisms is arranged on output-sides of the two sets of first and second change speed mechanisms and switches disconnection/connection of power transmitted from each of the two sets of first and second change speed mechanisms.
The first to third control valves of JP-A-2004-196106 are arranged on left and right side surfaces of the transmission case in a front-rear direction. That is, they are arranged on outer sides of the transmission case at positions corresponding to the hydraulic clutches provided in the transmission case. However, since the hydraulic clutches are arranged at proper positions of a power transmission mechanism in the transmission case, the first to third control valves are arranged in the front-rear direction, in many cases.
Therefore, the oil passage formed in the transmission case is also formed at various front and rear positions of the transmission case and a piping of the valves is lengthened, so that it is not easy to arrange the valves on the side surfaces of the transmission case. Also, it is necessary to long arrange the hydraulic pump at a side of the engine with respect to the control valves on the side surfaces of the transmission case, which has room for improvement.
According to the transmission of the tractor disclosed in JP-A-2008-95748, the advancing and reversing hydraulic clutch mechanisms are provided at an upstream side and the first and second hydraulic clutch mechanisms are provided at a downstream side with the main change speed mechanism being interposed therebetween, so that a main change speed multistage are implemented. However, JP-A-2008-95748 is the same as Patent Document, in that the hydraulic clutches are separated and arranged at the front and rear sides, which has room for improvement.